1. Field of the Invention
This invention relates to turbines for generating electric power. More particularly, this invention relates to turbines for generating electrical power which are driven by the force of the tides.
2. Description of the Related Art
For many years, men have sought a way to harness efficiently the power in ocean and river currents, and in the tides, which are governed by gravitational forces and are thus not subject to consumption by combustion as in the case of petroleum, coal and other natural resources. Numerous schemes, have been developed to harness the power in tidal waters and in ocean or river currents, but for a variety of reasons, none of these has been truly successful. For example, U.S. Pat. Nos. 3,604,942 to Nelson, 3,912,937 to Lesser, 3,922,012 to Herz, and 3,927,330 to Skorupinski all show systems for underwater turbines which involve blades that collapse when they are being dragged against the current and are supposed to open up again when disposed favorably with respect to the current, so that a net torque is produced, which can be used to drive a generator. These systems are all relatively complex, and it appears unlikely that they will be reliable for any great length of time, especially considering the harsh underwater environment of the ocean, which is not only corrosive but, of course, is also home to a wide variety of barnacles, kelp weeds and the like which attach themselves to mechanical parts and would, over time, tend to render them inoperable.
Other systems concerned with obtaining power from current or tidal flows include the devices shown in U.S. Pat. Nos. 4,095,422 to Kurakake (a system having very complex arrangement of a number of paddle wheels), 4,292,535 to Diggs (a complex system involving a number of swinging blades, for converting water power into electricity), and 4,023,041 to Chappell (a water-powered generator that floats up and down with the water level and rotates in response to changes in tide or current flow). All the systems shown in these patents are very complex, involving a large number of moving parts, and would be costly to manufacture and would appear unlikely to be reliable in operation.
Other patents which show water powered devices that may be of some historical significance, but which do not adequately solve the problem of obtaining suitable useful power from tides are U.S. Pat. Nos. 204,728 to Haskins; 958,467 to Bennett; and 1,320,650 to Pratt.
Many of the designs shown in the patents referred to above involve disposition of electrical generation equipment below the water line, which raises a host of difficulties. Similarly, many of these designs would tend to macerate fish swimming into them, no escape route for fish being provided.
More recently, in an article in Popular Science, Vol. 226, No. 1 (Jan. 1985), pp. 56 et seg., there was described a proposed system for obtaining electrical power from the tides. In this system, a tunnel was to be dug along a waterway having a high degree of tidal activity, such as in the Bay of Fundy. The tides are constrained to pass through the tunnel. Water is stored in a pond during the incoming tide and used to generate power on the outgoing tide only, although generation in both modes would be possible. A turbine is mounted for rotation within the tunnel, and is driven by water passing therethrough. The stator of a circular generator is disposed around the turbine in the wall of the tunnel and the rotor of the generator is affixed to the outer extremities of the blades of the turbine. This system appears, according to the Popular Science article, to have some utility. On the other hand, the turbine design employed places the electrical generation equipment in and closely surrounding the tunnel through which the water flows. This can be expected at best to pose maintenance difficulties, and is a serious constraint on the design of the generator. Furthermore, and as detailed in the article, many unpredictable environmental changes caused by the variation of the tides will inevitably occur if a project of this type having power generating capacity sufficient to justify its cost is constructed. Governmental approval may therefore not be possible, if the environmental impact appears likely to outweigh the benefits of the power provided.
Also discussed in the Popular Science article is a French project on the Rance River in which generators are disposed in bulbs disposed in the water stream, coaxial with the turbines which drive them. Apparently, this system has been in operation for some time, but the apparatus is quite expensive, as compared to that which is the primary subject of the article. The Rance River project also has had substantial environmental impact in that it relies upon variation of the natural tides for steady power, and suffers from many of the same design and maintenance problems.
The most desirable location for a tide driven turbine generation system would clearly be an oceanic area in which a large number of consumers of electric power are located in juxtaposition to an area having relatively large tidal variation. Such an area is the northeastern portion of the United States, where the population density is high, running from Washington, D. C. to Boston and beyond, and where the tides are also quite high. Several good spots are found along the coast of Maine and between Maine and Nova Scotia, in particular between Maine and Grand Manan Island which is nine miles off the coast of Maine. The tides in the channel between them, which is up to some 300 feet deep, run at up to approximately 3.4 mph with a normal variation of approximately 20-26 feet.
It will be appreciated by those skilled in the art that a supporting structure will be necessary to locate turbines and generators directly in and above the water respectively. It would be desirable to use such a structure for other purposes as well, e.g., as a causeway for vehicular traffic between the mainland and an island or other land mass between which the tides are relatively high. In this way, maximum utility could be provided by the tidal generation system according to the invention.